Network protection is an important characteristic of a telecommunication network. In order to realize the protection, a protection path, not joint (i.e., distinct from) with a working path, is usually established in advance. When a fault occurs to the working path, a working flow is switched from the working path to the protection path. Generally, a protection label switching path (LSP) is established with an exclusive bandwidth for each working LSP for protection. In this way, the protection bandwidth that needs to be reserved on a link is the sum of all the protection LSP bandwidths passing through the link so a large amount of bandwidth will be reserved and cannot be used for other services.
In fact, in most cases, a probability of multiple faults occurring at the same time is quite low. Therefore, shared mesh protection proposed subsequently is a method for realizing bandwidth sharing of a plurality of protection paths in the case of a single-point fault. The shared mesh protection is a type of end-to-end protection with the protection paths and resources allocated in advance. Thereby, shared mesh protection can achieve the protection switching speed of linear protection switching, and the switching speed is much faster than that of recovery protection which is typically used in current automatic switching optical networks (ASONs).
FIG. 1 is a specific example in which shared mesh protection technology in the prior art is applied. A network is constituted by nodes N1 to N6 and links between the nodes including five working LSPs (LSP1 to LSP5) and five corresponding protection LSPs (LSP6 to LSP10) and each of the LSPs is shown in FIG. 1. Table 1 is a database for calculating bandwidth reservation information for each link in the example which maintains bandwidths amount of the services need to be switched to another link when a fault occurs to one link in the network. If the switching succeeds, the link that is switched to is also required to reserve at least corresponding protection bandwidth. For example, the number “1” in the second row and fifth column indicates that 1 M service traffic is switched from a link L4 to a link L1 when a fault occurs to the link L4. For each link, only a maximal value of the bandwidth of the services switched during a fault of the link needs to be reserved to ensure that the link is able to carry the switched services completely in the case of a fault at any position.
TABLE 1MaximalReservedLinkL-1L-2L-3L-4L-5L-6L-7N1N2N3N4N5N6BandwidthL-111111L-211111L-311111L-41111111L-51111L-6121112L-71111111
In the prior art, a centralized control method is employed to calculate a reserved bandwidth. In a first method of the prior art, a centralized controller calculates routing and bandwidth information in the whole network and maintains entries similar to those in Table 1. When a protection path is computed, a protection bandwidth of each link on the protection LSP is obtained according to the entries. When a protection path is established, bandwidth information about each link is carried thereon. Therefore, nodes on the protection path are enabled to perform bandwidth reservation based on the information.
In a second method of the prior art, when a protection path is established, by carrying explicit routing information about a working path, each node maintains an entry similar to that in Table 1 according to the explicit routing information about the working path. However, the node just maintains the protection bandwidth information needed for links on the node itself. Each node determines required protection bandwidth for the links on the node itself according to the entry maintained by the node itself.
However, the first and second methods of the prior art only support the protection switching for a single fault. If a second fault occurs before a first fault is recovered (i.e., as available bandwidth information on the protection LSP has been changed after the first fault switching and the system lacks in managing and maintaining the shared protection bandwidth of the protection LSP), the second fault switching may fail and service protection may not be realized. In addition, in the first method of the prior art, the centralized controller further needs to maintain a large amount of information and requirements for the centralized controller are very high.
For follow-up protection after one fault, a simple approach is to recompute the shared protection path of the affected LSP and redeploy new protection paths. However, in such an approach, many LSPs are affected and the implementation is quite complicated as a large number of LSPs need to be removed and reestablished.